I believe you mis read. there is a switch right below the light assembly in the pic which i would assume is in the dash but inside the square where the light is there is another switch. is there a external next to the bulb that i dont know about?

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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
Monte carlo figure 8 car